Niagara BeamEmitterSetup script BeamID flick between -1 and LoopCount.

Development Rendering
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1

When using ribbon renderer in Niagara, I found BeamID is -1 in some frame, which make the ribbon effect broke.

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If change BeamID to keep same value when compare failed, the effect correct, is it right?

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2

Hi huafu hong,

Thank you for bringing this issue to our attention. I was able to repro an odd behavior of the resulting effect in UE 5.3 - 5.7 and source versions with the following steps:

  1. Create a new Niagara System/Emitter based on the “Static Beam” emitter
  2. On the “Particle Spawn” Stage:
    1. Delete the “Beam Width” Module
  3. On the “Emitter Update” Stage:
    1. On the “Emitter State” Module, set “Loop Duration” to 0.5
    2. On the “Beam Emitter Setup” Module, set “Beam End” to “Random Vector” with (Vector Scale = 100, Recalculate Random Each Loop = true)
    3. On the “Spawn Burst Instantaneous” Module, set “Spawn Time” to multiples of a frame: 1/60, 2/60, 3/60, 4/60... The result is correct for an even number of frames, but incorrect for an odd number of frames

Your proposed fix seems appropriate, although I believe some extra testing must be made with different combinations of emitter lifetime “Loop Behavior” and “Loop Duration”, which can affect the evolution of LoopCount. I have filed an internal bug report about this so that the engine devs can take a closer look. Here’s the tracking number: UE-368844 (the link should become accessible once the devs mark it as public).

Let me know if there is anything else I can help you with.

Best regards,

Vitor